Modeling turkey growth with the relative growth rate.

Six sigmoidal growth curves and two growth curves derived from a two-phase relative growth rate model were evaluated, using an experimental body-weight data from male and female turkeys of two genetic lines; a fast-growing (F) line and a randombred control (RBC) line from which the F line was developed. When their root mean square error was compared to the root mean square error of the local regression smoother, all sigmoidal growth curves: the logistic, Gompertz, von Bertalanffy, Richards, Weibull, and Morgan-Mercer-Flodin growth curves demonstrated a lack of fit. The primary source of the systematic lack of fit was identified with nonparametric estimates of the relative growth rate (the growth rate as a fraction of the body weight) of 20 turkeys. When the relative growth rate was estimated from the above sigmoidal growth curves, none could accommodate features of the nonparametric estimates of the relative growth rate. Based on the feature of the relative growth rate, two new growth curves were derived from a segmented two-phase model. Both models, in which the relative growth rate decreases in two linear phases with slopes of beta1 and beta2 joined together at time=kappa, gave growth curves that fit the experimental data acceptably. The linear-linear model with the smooth transition rendered better fit over the model with the abrupt transition. When the growth curves of male and female turkeys were compared, beta1, beta2, and kappa were smaller in males. When the F line was compared to the RBC line, beta1 and kappa were smaller and beta2 was closer to zero, indicating that the relative growth rate declined rapidly until about 61 days of age in the F line, while it declined less rapidly until about 71 days of age in the RBC line.

Third coronary artery bypass operations: risks and costs.

BACKGROUND: Third coronary artery bypass operations are technically difficult and are associated with increased risk. METHODS: We reviewed the cases of 469 patients who had undergone a third isolated coronary artery bypass operation and used univariate and multivariate testing to examine the effect of preoperative and operative variables on outcome and costs. RESULTS: The in-hospital mortality was 7.0% (33 patients). Advanced age and severe symptoms were found to increase risk (both p < 0.05): the mortality was 14% (n = 74) in patients 70 years old or older who had severe symptoms. However, the overall mortality for 1993 through 1995 was 4.3% (5/117) and only one death (1.3%) occurred among the 79 patients who were less than 70 years old. The late survival rate was 94%, 84%, and 66% at 1, 5, and 10 postoperative years, respectively, and predictors of decreased late survival were advanced age, abnormal left ventricular function, and diabetes (all p < 0.05). Again, age of 70 years or more was a predictor of a poor outcome. Only 52% of patients in that subgroup (including both early and late mortality) were alive 5 years after operation. Analysis of direct hospital costs showed that the mean costs of third coronary artery bypass operations were 21% higher than the mean costs of primary operations but that the elevation in the mean costs for third operations was related to very high costs in 4 patients. Sex was found to influence the cost of both primary and third operations (increased cost for women). CONCLUSIONS: Unfavorable outcomes after third coronary artery bypass operations have been associated with preoperatively definable variables, particularly age of 70 years or more. The in-hospital mortality in patients younger than 70 was low, and long-term survival in this group has been favorable. The increased hospital costs associated with third operations are related to high costs in only a few patients and have been unpredictable.

Body composition analysis of pigs by dual-energy x-ray absorptiometry.

Dual-energy x-ray absorptiometry (DXA) was evaluated as a method for measuring body composition of pigs. Forty-eight female pigs (10.2 to 60.5 kg) were killed and the whole bodies scanned on a DXA instrument. The DXA measurements provided readings of total tissue mass, percentage of fat, fat tissue mass, lean body mass, and bone mineral content. By chemical analysis, the whole body fat content of the pigs ranged from 9.3 to 24.3%, giving rise to DXA RST values (ratio of attenuation coefficients) ranging from 1.386 to 1.334. The average percentage body fat measured by DXA (18.2 +/- .9%) was not significantly different (P = .76) from the results by chemical analysis (17.8 +/- .6%); however, concordance correlation analysis revealed unacceptable accuracy in the DXA measurement due to a negative bias for smaller percentages and a positive bias for larger percentages. Total body fat measured by the two methods was also highly correlated (r = .989), and the average for DXA (7.31 +/- .62 kg) was not significantly different (P = .89) from the value for the chemical method (7.20 +/- .50 kg). The relationship between the DXA estimate of lean body mass and the amount of protein in the body by chemical analysis was described by the equation: kg protein = .227.kg DXA lean -1.28, with a correlation coefficient (r) of .968. The DXA measurements of total tissue mass and actual body weights were highly correlated (r = .999), with an acceptable concordance at the .05 level. Scans were also analyzed for regional composition of the front and back legs. It was generally difficult to determine anatomically how well soft tissue described by DXA regions corresponded to those dissected. The DXA and chemical results for regional analysis of back legs were in better agreement than those for the front legs. These results indicate that DXA may be used as a reliable method for measuring body composition of pigs, but needs more extensive calibration and may be more appropriate for total body rather than regional analysis.

Host-seeking of blacklegged tick (Acari: Ixodidae) nymphs and adults at the woods-pasture interface.

To clarify the risk of pastured livestock for exposure to Ixodes scapularis Say (Acari: Ixodidae), we estimated the host-seeking activity of nymph and adult blacklegged ticks at the woods-pasture interface on horse farms in Maryland. Parallel linear transects of 100 m length and 1 m width were sampled repeatedly in pastures and adjacent woodland locations during periods of nymph (early summer) and adult (fall and spring) host-seeking activity. Data collected over two successive years indicated that adults were most abundant in ecotonal vegetation at the wood's edge, median values of 6.4 and 2.2 ticks per 100 m2 sample during fall and 1.2 and 0.5 ticks per 100 m2 sample for spring periods. Nymphs were most abundant in the shallow woods location, median values of 4.2 and 35 ticks per 100 m2 sample, followed by the deep woods and wood's edge locations. Host-seeking nymph and adult black-legged ticks also were collected repeatedly in pasture vegetation, median values ranging from 0.2-0.8 ticks per 100 m2 sample, with a progressive decrease in abundance from the fenceline into pasture. Adults and nymphs both were uncommon more than 5 m into pastures, where only two adults and one nymph were captured in 84 (fall and spring) and 24 (summer) 100-m2 samples, respectively. Levels of adult and nymph host-seeking in pasture vegetation were spatially correlated with tick abundance in adjacent woodlands when ticks were numerous; this condition presumably reflects a spillover of ticks from the woodlands-based population. These findings expand knowledge of black-legged tick host-seeking behavior and establish a basis for the exposure of pastured livestock to nymphs and adults.

Targeted integration of the Ren-1D locus in mouse embryonic stem cells.

We have introduced a Ren-1D targeting vector into embryonic stem cells containing the two highly homologous mouse renin genes Ren-1D and Ren-2. Using a polymerase chain reaction (PCR) screen designed to detect targeted integration at Ren-1D and Ren-2, we isolated 15 targeted embryonic stem cell clones, all of which had undergone a gene conversion event at the Ren-1D locus. We did not isolate any clones in which the incoming DNA had recombined with Ren-2. Over the region encompassed by our transgene, Ren-1D and Ren-2 display greater than 95% homology. Our results suggest that the machinery driving gene targeting by means of homologous recombination in mammalian cells is capable of distinguishing between these two sequences. Construction of transgenic mice with the embryonic stem cells reported here carrying a mutated renin gene will permit a greater understanding of the functions of the Ren-1D and Ren-2 gene products and their relative contribution to cardiovascular homeostasis.

Identification of epitopes recognized by monoclonal antibodies SM1 and SM2 which react with all pili of Neisseria gonorrhoeae but which differentiate between two structural classes of pili expressed by Neisseria meningitidis and the distribution of their encoding sequences in the genomes of Neisseria spp.

The pili expressed by all isolates of Neisseria gonorrhoeae react with two monoclonal antibodies, SM1 and SM2. In contrast, although many isolates of Neisseria meningitidis also express pili (class I) which react with antibodies SM1 and SM2, a proportion express pili (class II) which fail to react. In order to define the epitopes recognized by these antibodies, a series of overlapping peptides corresponding to the amino acid sequence of conserved regions of gonococcal pili have been synthesized. The minimum epitope recognized by antibody SM1 was found to comprise a linear peptide EYYLN, corresponding to residues 49-53 of mature pilin. In contrast, antibody SM2 reacted with a number of peptides from around the cysteine residue (Cys 1) at position 120, suggesting that an extended region may contribute to a conformational epitope recognized by this antibody in the native protein. The identification of the two epitopes defines structural differences between the classes of pili expressed by meningococci. In order to determine the distribution of pilin gene sequences in Neisseria we used as hybridization probes an oligonucleotide (PS1) with the sequence 5'-GAGTATTACCTGAATCA-3' which spans the coding region for the SM1 epitope, and a fragment of the 3' end of the gonococcal pilE gene which contains conserved sequences flanking the two Cys codons and encodes the SM2 epitope. All strains of N. gonorrhoeae and N. meningitidis tested, regardless of piliation phenotype, harboured DNA sequences homologous to those encoding the carboxy-terminus of meningococcal class I pilin. Furthermore, all gonococci and all meningococci producing class I pili hybridized with oligonucleotide probe PS1. Non-reverting non-piliated derivatives of previously class I pilus-producing strains showed reduced hybridization signals with this probe, but nevertheless retained sequences homologous to the coding sequence for the SM1 epitope. However, meningococci producing class II pili could be divided into two groups on the basis of their reaction with the PS1 probe: half the strains tested failed to react, which is consistent with our previous analysis of silent class I pilin sequences; the remainder reacted (relatively weakly) with the probe, suggesting that the silent pil sequences in these strains extend further towards the 5' end of the pilin gene than in strains studied previously. Some strains of Neisseria lactamica reacted weakly with both types of probe but failed to produce SM1-reactive pili. In contrast, isolates of Neisseria flava, Neisseria pharyngis, Neisseria sicca and a series of unrelated bacteria failed to react with both SM1 antibody and the DNA probes. This confirms that possession of 'gonococcal' pilin sequences is limited to the pathogenic neisseriae.

Nucleotide sequence of the structural gene for class I pilin from Neisseria meningitidis: homologies with the pilE locus of Neisseria gonorrhoeae.

The nucleotide sequence has been determined for the expressed pilin (pilE) locus of Neisseria meningitidis strain C311 which produces class I pili that are antigenically and structurally similar to those of gonococci. The deduced amino acid sequence of the N. meningitidis pilE translation product contains a 7 amino acid N-terminal pre-pilin leader sequence which is identical to that found in gonococcal pilin and which is characteristic of N-methylphenylalanine pili in general. The succeeding N-terminal 53 amino acids are identical to those found in the equivalent position in antigenically variant gonococcal pilins and confirm direct peptide sequencing of the amino-terminus of at least one type of meningococcal pilin. Other regions that are conserved in variant pilin polypeptides from Neisseria gonorrhoeae are conserved at the amino acid level in the class I meningococcal pilin but the coding DNA contains numerous base substitutions when compared with the equivalent gonococcal pil sequence. Sequences extending downstream for about 140 bp on the 3' side of the coding region for both pilin genes are only about 85% homologous.

Improved methodology for generating controlled test atmospheres.

Improved methodology has been developed for generating controlled test atmospheres. Vaporization of volatile liquids is accomplished in a 28 mm (O.D.) glass J-tube in conjunction with a compressed air flameless heat torch, a pressure-sensitive switch, and a positive displacement piston pump. The vaporization system has been very reliable with a variety of test materials in studies ranging from a few days to several months. The J-tube vaporization assembly minimizes the possibility of thermal decomposition of the test material and affords a better margin of safety when vaporizing potentially explosive materials.

Biological properties of aspartame. I. Evaluation of central nervous system effects.

Aspartame was administered intragastrically to rodents at doses between 10 and 550 times the expected daily human intake to evaluate the effects on central nervous system function. No biologically meaningful effects were observed in either rats or mice following acute administration by the intragastric route. Aspartame administered as 9% of the diet (about 11 g/kg/day) for thirteen weeks to weanling rats altered the learning behavior of male rats. This effect of impaired learning behavior was nearly identical to that observed for an approximately equimolar amount of L-phenylalanine. The learning behavior of the female rats was not altered by either L-phenylalanine or aspartame at these extremely large doses. It was concluded that prolonged dietary ingestion of aspartame at levels approximately 550 times that expected for normal human daily ingestion was necessary to elicit a behavioral deficit.

An apparatus for generation of vapors from liquids of low volatility for use in inhalation toxicity studies.

While it is usually a simple matter to perform inhalation exposures to vapors from low-boiling liquids, inhalation exposures to vapors of high-boiling liquids present problems, especially the risk of decomposing the test substance by use of excessive heat. This work describes a device for the volatilization of high-boiling liquids, in a manner suitable for conducting inhalation exposures, without requiring heat input, which avoids this difficulty. The device is based on counter-current volatilization employing a multi-plate high efficiency distillation column. The column is thermostated below ambient temperature, which increases stability of operation and flexibility of application.

2-Isocyanatoethyl methacrylate--an inhalation dominant lethal study in the male Sprague-Dawley rat.

2-Isocyanatoethyl methacrylate (IEM), a monomer, has been developed for use as a component in coating materials. The dominant lethal test was used to evaluate the mutagenic potential of IEM in rats. In this study, male Sprague-Dawley rats were exposed to 0, 25, 80, or 250 ppb of IEM by inhalation for 6 hr/day for 10 weeks (one spermatogenic cycle). After the exposure period, the males were bred with untreated virgin female rats. At approximately mid-gestation, the females were sacrificed and the number of corpora lutea, implantations, and resorptions were recorded. Statistical analysis of these data indicated that the treated males were comparable to control males in all reproductive parameters evaluated. IEM did not affect male fertility or produce dominant lethal mutations in male rats following ten weeks of inhalation exposure to 25, 80 or 250 ppb IEM.